<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>my css2</title>
    <style>
        .c1 {
            border: 1px solid black;
            width: 50%;
        }
        html {
            font-size: 20px;
        }
        .c2 {
            font-size: 30px;
        }
        .c3 {
            font-size: 2em;
        }
        .c4 {
            font-size: 2rem;
        }
        .c5 {
            color: rgb(100, 100, 100);
        }
        .c6 {
            color: blue;
        }
        .c7 {
            /*color: #1133aa;   !*可以简写为下面形式*!*/
            /*color: #13a;*/
            color: #d65111;
        }
    </style>
</head>
<body>
<h2 class="c5">云计算 1907</h2>
<h2 class="c6">云计算 1907</h2>
<h2 class="c7">云计算 1907</h2>
<h2>云计算 1907</h2>
<h2>云计算 1907</h2>
<p class="c2">
    <span class="c3">云计算 1907</span>
    <span class="c4">云计算 1907</span>
</p>
<div class="c1">
    这是一个测试div
</div>
</body>
</html>